One of the greatest problems facing wireless network operators is the need to serve large numbers of customers with varying needs using the infrastructure available to them. Numerous considerations affect the number of customers that may be served by a particular set of resources, and constant efforts are being directed toward improvements in efficiency. Various mechanisms for improvement of communication efficiency involve management of handover from one cell to another. Handover typically occurs when a handover threshold between two cells is reached, such as around the point where the difference between the reference signal received power (RSRP) or reference signal received power (RSRQ) of a neighbor cell and the serving cell becomes greater than a threshold. Numerous conditions exist that may affect the proper setting of a handover boundary, and one condition of particular note is a difference in load or user location or distribution between the two cells involved in the handover. A number of signaling mechanisms exist between cells, such as the widely used X2 interface defined in the Third Generation Partnership Project (3GPP) standards, for example, 3GPP TS 36.420—Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 general aspects and principles, 3GPP TS 36.421—Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 layer 1, 3GPP TS 36.422—Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 signaling, and 3GPP TS 36.423—Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 application protocol (X2AP), and such signaling mechanisms can be used to communicate load information between cells.
One important type of cell combination calling for proper accounting for load is a combination of heterogeneous cells, such as macro and pico cells. A number of pico cells may operate within the boundaries of a macro cell, and the difference in ranges between macro and pico cells can lead to significant load imbalances. For example, a user equipment (UE) may be within the boundaries of a pico cell while still being well within the boundaries of a macro cell. If threshold calculations designed to account for cell-edge conditions are used, a UE assigned to a macro cell might not be handed over to a pico cell because the threshold conditions would not be encountered. Such an approach would lead to overloading of macro cells and underloading of pico cells. Load variations may be encountered between macro cells and between numerous other types of cell combinations. The overall throughput, and gains in throughput that may be expected from a handover, will be affected by load in many instances. Therefore, various mechanisms have been and are being developed to take loading into account when determining handover thresholds.